Problems encountered in crude oil production include the precipitation and/or agglomeration of particles or substances in solution and/or in suspension in the produced formation fluid. The term particles, is defined herein includes, but is not limited to solid particles, emulsion droplets, and gas bubbles. Asphaltenes are examples of solid particle components of crude oil that are often found in colloidal suspension in the formation fluid. If for any reason the colloidal suspension becomes unstable, such as with a drop in fluid pressure, the colloidal particles will precipitate, stick together and, especially in circumstances where the asphaltenes include resins, plug the well. Asphaltene precipitation during production causes severe problems. Plugging of tubing and surface facilities disrupts production and adds cost. Plugging of the formation itself is very difficult and expensive to reverse, especially for a deep water well.
Asphaltenes can precipitate from crude oils during production of the crude oil due to a drop in pressure. Crude oils which are somewhat compressible are particularly susceptible to this effect because the reduction in dielectric constant per unit volume which accompanies fluid expansion causes the asphaltene suspension to become unstable. The onset of asphaltene precipitation is difficult to predict, and when asphaltene plugging happens, it usually happens unexpectedly. Advance warning of asphaltene precipitation based on laboratory testing of formation fluid according to present techniques, while useful, is not optimally reliable.
Formation gas may be contained in solution in the produced formation fluid and may come out of solution as the fluid pressure is reduced during transit of the fluid out of the well.
Attempts have been made to determine the onset of the particle precipitation, particularly asphaltenes. U.S. Pat. No. 5,969,237 to Jones et al. describes a system for detecting scattered acoustic energy to determine particle size distribution of asphaltene particles. U.S. Pat. No. 6,087,662 to Wilt et al. uses mid-range infra red absorption spectroscopy to determine asphaltene concentrations in hydrocarbon feed. U.S. Pat. No. 5,420,040 to Anfindsen et al. provides a system to measure changes in the conductivity or capacitance of a petroleum fluid for determining asphaltene precipitation in the fluid.
All of the prior art systems infer particle precipitation and other related characteristics from related physical measurements. There is a demonstrated need for a system to view and analyze the particles to more definitively determine the characteristics of the particles.